QB - quarterback.
SB - super back, "someone that ... the quality that we're looking for for this player, so we call him our super back."
F - true fullback.
A - Slot receiver. "You'll see it a lot when people go in. It's a different type of player to play slot receiver. Like Wes Welker of New England is a tremendous slot receiver. Why? It's his ability and the intermediant zone to have a good feel for zone or man, his foot work, quick moves, quick cuts, guys that can cut well are usually what you see at a slot receiver position."
Z - strong side wide receiver.
X - weak side wide receiver or split end.
T - tackles
G - guards
C - center
Y - true tight end
U - move tight end

"At the end of the day, what you'd like is for your U and your F to be the same type of guy," Marrone said. "So your U and your F are the same, OK. And really this position that's A is really coming from these two positions."